The present disclosure relates generally to heating, ventilation, or air conditioning (HVAC) systems for a building. The present disclosure relates more particularly to a HVAC system configured to operate in a free cooling state and a mechanical cooling state.
Free cooling is a cooling technique which uses low temperature outside air to provide cooling for a system without requiring the use of chillers. Free cooling can be used as an alternative to mechanical cooling (e.g., vapor compression cooling) under certain weather conditions. When free cooling is used, the chillers providing mechanical cooling can be deactivated and cooling towers used to provide free cooling.
In traditional free cooling systems, free cooling is used whenever the outdoor wet bulb air temperature is below a minimum temperature required for free cooling. However, the traditional approach does not take into account the economic cost associated with transitioning between free cooling and mechanical cooling. For example, switching between a mechanical cooling state and a free cooling state may incur an economic cost. It would be desirable to provide a HVAC system which uses economically optimal control to transition between a mechanical cooling state and a free cooling state.